Roof bolts for use in mines generally include an elongated bolt having an expansion member for engagement with the roof strata at a point remote from the bolt head. Most mine roof bolts are now made with rolled threads and, in the process of rolling the threads the end of the bolt is deformed into a generally smooth concave configuration, the outer periphery thereof being jagged. In use of such bolts with expansion shells of the type embodying expansion members, a wedge member for actuating the expansion members and a stop member against which the threaded end of the bolt abuts, problems have been encountered affecting the proper installation of the assembly in the mine roof opening. The rotation of the bolt against the stop member to actuate the expansion member sets up friction between the stop member and bolt, with resultant galling of the stop member due to the frictional engagement of the jagged peripheral edge which bears on the stop member. In turn, this causes the expansion member to spin in the bolt hole, instead of expanding and properly engaging the mine roof strata.
It is an object of this invention to provide a mine roof bolt assembly embodying a roof bolt to which is threadedly engaged an expansion member, wherein a minimum of friction is produced between the mine roof bolt and expansion member, thereby allowing relative rotation of the roof bolt with respect to the expansion member and facilitating the installation of the mine roof bolt assembly in the mine opening.
Another object is to provide a mine roof bolt assembly of the character described wherein a portion of the stop member of the expansion member engages the central concave portion of the roof bolt end, the stop member being in spaced relation to the jagged peripheral edge thereof, thereby preventing galling of the stop member and undue friction between the roof bolt and expansion member.
A further object is to provide a mine roof bolt assembly of the character described wherein the stop member includes a substantially planar tab, the central portion of which is struck downward to provide an indentation which engages the central concave portion of the bolt end.
Other objects will be apparent from the following detailed description of the invention taken in conjunction with the appended drawing.